Refractory heat-insulating material and method of making the same



Aug. 28, 1928. 1,682,675-

B. T. HORSFIELD REFRACTORY HEAT INSULATING MATERIAL AND METHOD OF MAKINGTHE SAME Filed Dec. '7, 1925 l l l i I I l Ll gvwento'c Gummy PatentedAug. 28, 1928- UNITED STATES PATENT OFFICE.

M811 T. HORSI'IILD, O1 BADIN, NORTH CAROLINA, ASSIGNOB TO um 00!- rm 01'names, 0! PITTSBURGH, PIXNSYLVANIA, A. CORPORATION 0] P331)!- SYLVANIA.

immcroair m'r-msvmrme mum AND imrnon or mute an sum Application fledDecember I, 1985. Serial No. 78,888.

= least become incapable of carrying a working load at temperatures alittle above redheat.

Another object is to provide a refractor heatinsulating material or bodywhich can produced at reasonable cost and readily fashioned intopractically any desired shape, as for example in situ to form the liningof a furnace or kiln or in blocks or the like for laying a linin orwall. A further object is to provide a re actory body which, possessingthe advantages named above, shall also be light in weight. a

The accompanying drawing shows, roughly, one embodiment of theinvention.

The essential ingredient of this embodiment is a hi h melting oxide,preferably aluminum'oxi e, or a mixture of such oxides, in the form ofrelatively small particles each containin at least one void. Theseparticles, wit or without the addition of other refractory material, areagglomerated or bonded together into a firmly coherent mass by means ofa suitable binder, which may be, for example, sodium silicate, sodiumaluminate, calcium aluminate, or bonding clay, with enough water to makethe mass conveniently plastic. While the mass is still plastic it may beshaped to the desired form, as by tamping in a mold, after which it isdried and baked. Molding under pressure is often desirable, as giving astronger article'p0ssessing greater compression strength than one whichis merely tamped in the mold. One of the important factors to beconsidered in selecting a binder or bonding agent is its possiblefluxing effect on the alumina or other oxide particles at thetemperatures to which the material will be subjected in use, and alow-fluxing binder is therefore usually desirable, that is, a binder ofsuch character or so regulated in amount, or both, that the blocks cansafely withstand the temperature conditions of use.

A simple and practical method of convertmg an oxide, for instancenatural alumina, or a mixture of oxides, as for example, lime, magnesiaand alumina, into the form of small v01 -conta1n1ng particles or bits isdescribed at length in my copending application Serial No. 12,617, filedMarch 2, 1925. In the method there described the alumina is dischargedfrom the furnace, in which it is fused, in the form of a relatively thinstream and is met by a transverse air or steam jet, by which it 1s blowninto fragments. Upon'examination these fragments are found to be hollowglobules, ran mg in size from very fine sand to one-eight orthree-sixteenths of an inch or more, in diameter, with walls which donot as a rule exceed one one-hundredth of an inch in thlckness and arein most cases much thin.- ner:-*In general the hi her the velocity ofthe blast the finer the glo ules, and I have observed that if thevelocity is too low any oxidizable substances in the alumina may not, inthe case .of the larger globules, be as completely oxidized as when ahigher velocity is used, and may contain larger amounts of H011. Suchlarger granules are dark gra or black in color i containing much freecar on, and may be from one-fourth to one-half inch in diameter, andalthough hollow like the smaller ones they are apt to be quite irregular1n shape. While I havesuccessfully used air and steam at pressures ran'ng from fifty to one hundred and fifty poun er s uare inch, the higherpressures are pre erre as bein less likely to produce insufiicientlyoxidize granules, especially when the stream of molten alumina is undulyviscous. I also prefer to have the temperature of the alumina well abovethe melting point, primarily to insure adequate fluidity of the stream.In making a carbon-free product from alumina containin excess carbon(added to reduce undesired oxldes present in the natural ore) thissuperheating is desirable for the reason that it facilitates theoxidation of the carbon, both by the gas used for the blast (where, asis preferred, an oxidizing gas, as for example air or steam, isemployed) and also by the air into which the alumina is blown.

It is well known that in blowin blast furnace slag there is produced abrous material commercially known as sla wool, together with a largeamount of sma l glassy pellets. This seems to be due to the property onp 'of silicate slags by virture of which they pass through a pasty stagein cooling from the liquid to the sol1d state, so that as they arecooled in the air blast they are drawn out into the threadscharacteristic of slag wool. I believe this condition is characterlsticof the silicates and not of pure high-melting oxides which aresubstantially free from silica, and as a matter of fact I have been ableto produce like phenomena with molten aluminum oxide by adding about 5per cent of silica. If, therefore, it is desired to avoid all productionof threadlike forms the material to be treated should be low in silicaand other substances which do not crystallize promptly when theirtemperature is reduced to or below the freezing point. Where it isnecessar or desirable to remove silica from the oxide any convenientmethod for the purpose can be employed, as for example by treatment ofthe bauxite or other aluminous material with a carbonaceous reducingagent at a suitable temperature in the presence of iron, to reducesilica and cause the resulting silicon to alloy with the iron, asdescribed in the patent of William Hoopes, Francis C. Frary and J uniusE. Edwards, identified hereinafter.

For the purpose of my present invention I prefer, as a rule, small1globules, none larger than will pass throug a 20-mesh screen. Withlarger globules the molded blocks are lighter in weight and requirerather less of the bondin material but on the'other hand they have essresistance to crushing pressure; though in many cases the difference istoo slight to be important, due to the fact that the walls of theglobules, even when the latter are very large, say a quarter orfivesixteenths of an inch in diameter, are remarkably tough and stron inspite of their extreme thinness. In ma ing the globules the factorsgoverning the size thereof can be regulated to give approximately thedesired size, and sieves or screens may then be used to separate thosewhich are too large for the particular purpose in hand.

The amount of sodium silicate or other binder required to give adequatecoherence to the material depends in general upon the strength desiredand the permissible fluxin effect, and is therefore variable within widelimits. In any case the proportions suitable for a given use can readilybe determined by trial.

For making blocks, bricks, or other shapes, the plastic mixture istamped or pressed in suitable molds, dried, and baked. In drying theblocks a relatively low temperature is preferred, say not above 150 C.In baking a tem erature of 1000 to 1050 C. has been foun satisfactory,but much higher temperatures ma be employed and are in general preferreA brick made in this manner is illustrated in the accompanying drawingbut the illustration is rather imperfect owing to the limitations of penand ink as a medium for accurately picturing minute structures except atsuch lar e ma ifications as are apt to be mislea ing. t will beunderstood, however, that the appearance to the eye is not important,the drawing being furnished merely to indicate in a general way that atleast one of the major constitutents of the, referred material is in theform of small globules or pellets.

Globules of aluminum oxide are particularly suitable for my purpose.Bauxite or other crude alumina-bearing material can be purified formaking such globules, as for example by the process described in mycopending application above mentioned or in the United States patent ofWilliam Hoopes, Francis C. Frary and Junius E. Edwards, No. 1,534,316,issued April 21, 1925. As stated above, other oxides may be used,however, when their properties render them desirable.

The following specific examples of m invention are given as showing some0 the results so far obtained.

A. Globular alumina, no globules larger than about 20-mesh size, 97.5per cent; liquid sodium silicate 2.5 per cent, containing,approximately, sodium oxide 6.4 per cent and silica 24.7 per cent.Molded under pressure of 10,000 pounds per square inch and baked at 1400C. After four hours baking the compression strength of the brick was3585 pounds per square inch. With 5 per cent of the sodium silicate andcorrespondingly less globular alumina, with a baking temperature of 1400C. as before, four hours baking gave a compression strength ranging from4886 to 5030 pounds per square inch; eight hours, 4955; twelve hours,5695; sixteen hours, 7285. With 10 er cent of the sodium silicate, fourllolllls ba ing gave 6980 pounds per square inc 1.

B. Globular alumina, no globules larger than about 20-mesh size, 97.5per cent; sodium aluminate 2.5 per cent, containing, approximately,sodium oxide 23.6 per cent and alumina 43.8 per cent. Molded under10,000

g pounds per square inch. Baked four hours at 1400 C. the compressionstren th was 2095 pounds per square inch. Witi 5 per cent and 10 percent of the sodium aluminate, and correspondingly less of the alumina,four hours baking gave 3695 and 5665 respectively.

C. Globular alumina, no globules larger than about 20-mesh size, 97 .5per cent; bonding clay 2.5 per cent. Molded under 10,000 pounds persquare inch. Baked four hours at 1400 C. Compression strength, 4735pounds per square inch. With 5 per cent and 10 per cent of the clay, andcorrespondingly Ill , amounts of the binder, which in a number ofexperiments ranged from 12.6 per cent to 57.6 per cent. he compressionstren be varied from 1345 pounds per square inc to 2386.

Replacing part of the globular alumina with solid particles gives asomewhat stronger but heavier article, but even with a substantialproportion of solid particles the article need not weigh, in general,more than about two-thirds as much as standard alundum, magnesite orchromite bodles of I the same size. These solid particles may; be owproduced b crushing or grinding ho alumina glo ules, or by crushing orgrinding ordinary alumina solidified from the molten state withoutblowing. In' the examples iven above a relatively small amount of rokenlobules was present. In general, if the bric is to be used chiefly forits heatinsulating properties, I prefer to use a maximum of unbrokenglobules or, in general, alumina containing a substantial pro ortion ofvoids; whereas if it is to be used argely for its refractory character Iwould give it a higher proportion of particles without voids. The latterparticles may be alumina solidified from the molten state and crushed orground to the desired size, or it may be crushed globules, or both.

I claim: l 1. The method of'making a refractory material, comprisinmelting a refractory oxide, changing t e molten oxide into the form ofstrong hollow substantially spherical globules, and bonding the samewith a refractory binder.

2. The method terial, comprising melting a refractory oxlde and blowingthe same into the form of stron hollow substantially spherical globules,an bonding such globules together with a lowfluxin binder into acoherent body.

3. '51s method of making refractory material, com rising treating fusednaturally occurrin a umina to remove non-aluminous oxides t erefrom,blowing the treated alumina into the form of strong hollow substantiallyspherical globules, and bondingsuch lobules together with a low-fluxing"binder into a coherent body.

of making refractory ma-,

terial, comprising blowin into the form of hollow globules a stream 0molten refractory oxide, and bonding such globules to e'ther Ivsvifih alow-fluxing binder into a co erent 5. The method of making refractormaterial, comprising blowing mto the orm of hollow globules a streamofanolten alumina low. in silica, and bonding such globules with sodiumaluminate into a coherent body.

6. The method of making refractory material, comprising conv'ertinalumina into hollow lobules, mixing wit such globules a 1owuxing binderto form a more or less plastic mixture, and shaping and baking suchmixture to form a coherent body.

7. The method of making refractory mate rial, comprisin converting fusedalumina into strong ho low substantially spherical lobules mixingtherewith a binder and alumma particles substantially free fromvoids,and shapin and baking such mixture to form a coherent body.

8. The method of makingrefractory material, comprisin converting moltenalumina into hollow glo ules; mixing therewith like globules crushed orbroken, and a binder to make a plastic mixture, and shaping and bakingthe mixture to form a coherent body.

9. The method of making refractory material, comprising shaping underhigh pressure a plastic mixture composed at least in part of hollowsubstantiall spherical particles of alumina, and a bin er, and baking ata high temperature the bod so formed.

10. The method 0 making refractory material, comprising shaping underhigh pressure a mixture composed at least in part of hollow globules ofalumina, and sodium aluminate, and baking at a high temperature the bodyso formed.

11. The method of making refractory material, comprising shaping underpressure of approximately ten thousand pounds per square inch a mixturecontaining hollow globules of alumina, and sodium aluminate, and bakingthe body so formed at a temperatuifia of approximately 1400 C.

12. The method of making refractory material, comprising shaping amixture composed at least in part of hollow substantially sphericalparticles of alumina, and a sodium compound as a bonding agent, andbaking the body so formed.

13. A refractory body, composed largely of hollow substantiallyspherical particles of high-melting oxide, and binding material.

14. A refractory body, composed of alumina particles bonded with asodium compound, a large proportion of the alumina particles beinghollow and substantially spherical in form.

gave 4. The method of making refractory ma- 68 15. A refractory bodycontaining strong strong ules of high-melting oxide low in silica,bonded with a low-fluxing sodium compound.

17. A refractory body comprising hollow globules of alumina bondedtogether with a inder having insufiicient fiuxing effect to causesoftening of the bod at the temperatures to which such body is to besubjected in use.

18. A refractory body comprising hollow globules of low-silica aluminabonded together with sodium aluminate in amount insufficient to causesoftening of the body at the temperature to which the same is to besubjected in use.

19. A refractory body composed essentially of bonded strong hollowsubstantially spherical globules of refractory oxide low in silica.

20. A refractor body composed at least in part of bonded ho lbw globulesof alumina.

21. A refractory body composed at least in part of alumina and sodiumilluminate, the

former being at least chiefly in the form of hollow globules and thelatter serving to bond such globules together.

22. A refractory body composed at least in part of void-containingarticles of alumina, and a binder, said ref i 'actory body being capableof withstanding a temperature of 1500 C. and having a compressionstrength exceeding 2000 pounds per square inch.

23. A refractory body composed at least in part of void-containingparticles of alumina, and sodium aluminate as a binder, said refractorybody being capable of withstanding a temperature of 1500 C. and having acompression strength exceeding 3000pounds per square inch.

24. A refractory body composed at least in art of hollow globules ofalumina solidified rom the molten state, and a binder, said refractorybody being capable of withstanding a temperature of 1500 C. and having acompression strength exceeding 2000 pounds per square inch.

In testimony whereof I hereto affix my signature.

BASIL T. HORSFIELD.

